How to manage relative bradycardia (slow heart rate) in a patient?

Management of Relative Bradycardia

Relative bradycardia should be treated with atropine 0.5 mg IV every 3-5 minutes (maximum 3 mg) as first-line therapy when it causes hemodynamic instability or significant symptoms. 1, 2

Definition and Assessment

Relative bradycardia refers to a heart rate that is inappropriately slow for the clinical condition, typically <50 beats per minute, though the absolute number is less important than its appropriateness for the patient's clinical state 1, 2.

When to Treat

• Treat when bradycardia causes:
  • Hemodynamic instability
  • Acute altered mental status
  • Ischemic chest discomfort
  • Acute heart failure
  • Hypotension or shock
  • Syncope or presyncope
  • Dizziness or lightheadedness
  • Confusion due to cerebral hypoperfusion
  • Fatigue or exercise intolerance 1, 2

When Not to Treat

• Asymptomatic bradycardia
• Physiologic bradycardia (athletes, during sleep)
• Bradycardia appropriate for clinical condition 2

Treatment Algorithm

Step 1: Identify and Address Reversible Causes

• Medications (beta-blockers, calcium channel blockers, digoxin)
• Electrolyte abnormalities
• Hypothyroidism
• Increased intracranial pressure
• Infectious diseases (typhoid fever, Legionnaires' disease) 2, 3

Step 2: Acute Management for Symptomatic Bradycardia

1. First-line treatment:

   • Atropine 0.5 mg IV every 3-5 minutes (maximum total dose 3 mg) 1, 2, 4
   • Atropine works by blocking parasympathetic effects on the heart, increasing heart rate 4
   • Caution: Doses <0.5 mg may paradoxically worsen bradycardia 1

2. If atropine ineffective:

   • Epinephrine (2-10 μg/min) or Dopamine (2-10 μg/kg/min) infusion 2
   • Consider transcutaneous pacing for persistent symptomatic bradycardia 1

3. For specific situations:

   • Calcium channel blocker overdose: Calcium (10% calcium chloride 1-2g IV) 2
   • Beta-blocker overdose: Glucagon (3-10mg IV with infusion of 3-5mg/h) 2
   • Spinal cord injury-related bradycardia: Consider theophylline or aminophylline 1

Step 3: Definitive Management

• Temporary transvenous pacing: Reasonable for persistent hemodynamically unstable bradycardia refractory to medical therapy 1

• Permanent pacemaker: Consider for:

  • Persistent symptomatic bradycardia not responding to medical therapy
  • High-grade AV block or third-degree AV block
  • Symptomatic Mobitz type II second-degree AV block 1, 2

Special Considerations

Specific Clinical Scenarios

1. Post-heart transplant bradycardia:

   • Atropine may be ineffective due to denervation
   • Consider theophylline or aminophylline 1

2. Inferior myocardial infarction with bradycardia:

   • Atropine is first-line therapy
   • If unresponsive, consider theophylline (100-200 mg slow IV) 2

3. Relative bradycardia in infectious diseases:

   • Common in typhoid fever, Legionnaires' disease, and Chlamydia pneumonia
   • Treatment should focus on the underlying infection 3

Efficacy of Treatment

Approximately 50% of patients with hemodynamically unstable bradycardia respond to atropine therapy with either partial or complete response. Patients with sinus bradycardia tend to respond better to atropine than those with AV block 5.

Monitoring During Treatment

• Continuous cardiac monitoring
• Frequent blood pressure measurements
• Reassessment of symptoms
• Target heart rate >50 bpm 2

Pitfalls and Caveats

• Avoid atropine in patients with cardiac transplantation as it may paradoxically worsen bradycardia 1
• Use atropine cautiously in acute coronary ischemia or MI as increased heart rate may worsen ischemia 1
• Avoid relying on atropine in type II second-degree or third-degree AV block with new wide-QRS complex 1
• Temporary transcutaneous pacing can be painful in conscious patients and should be considered a temporizing measure 1
• Do not treat asymptomatic bradycardia or bradycardia appropriate for the clinical situation 2